Blade housing for low friction rotary knife

ABSTRACT

A power operated knife comprises a blade supporting structure supporting an annular blade for rotation about a central axis. The blade and blade supporting structure are engagable along bearing contact locations that are spaced apart in a direction parallel to the axis so that the blade is stabilized both radially and axially as the knife operates. The blade supporting structure comprises a split blade housing member that is radially expandible and contractible to receive the blade. The split blade housing member and blade engage along relatively short lines of bearing contact that serve to minimize friction and blade heating when the knife operates. The bearing locations are spaced apart both circumferentially around the blade perimeter and in the direction of the axis so that the blade position is stabilized during operation of the knife.

This is a Divisional application of application Ser. No. 09/120,778,filed on Jul. 22, 1998 now U.S. Pat. No. 6,769,184.

FIELD OF THE INVENTION

The present invention relates to power operated rotary knives and moreparticularly to a power operated rotary knife wherein a rotatableannular blade is supported for rotation about a central axis by a bladesupport structure providing bearing contact that minimizes bladevibration and heating.

BACKGROUND OF THE INVENTION

Power operated rotary knives have been in wide-spread use in meatpacking and other commercial food processing facilities. These knivesusually comprised a handle and a blade housing that supported an annularknife blade. The knife blade was driven about its central axis relativeto the blade housing by a motor via a gear train.

The knife blade comprised an annular body, a blade section projectingaxially from the body and driving gear teeth projecting axially from thebody oppositely from the blade section. The blade housing maintained theblade in position relative to the knife as the blade rotated. The bladewas subjected to various forces created by both the drive transmissionand the cutting action of the knife.

In some knives the blade housing defined a blade supporting race in theform of a peripheral groove that was rectilinear in cross sectionalshape for receiving the blade body and gear teeth. These blade housingswere frequently split and were resiliently expandable to receive theblade. The blade body and gear teeth were shaped to confront the axiallyopposite blade race sides with running clearance just sufficient toprevent the blade from binding in the groove. Consequently the blade andblade housing were slidably engaged over relatively wide contact areas.

In some other knives the blade housings had a radially inwardlyextending lip that defined a frustoconical surface engaging afrustoconical blade surface to prevent the blade from separating axiallyfrom the blade housing. In such cases, the knives also comprised a shoethat pivoted into engagement with the blade. The shoes also providedfrustoconical surfaces that wedged the blade toward the blade housingand retained the blade in place.

Some prior art rotary knives tended to vibrate undesirably in usebecause the blade rotation axis was permitted to shift relative to theblade housing. Put another way, the blade tended to bounce around withinthe blade housing so that the entire knife vibrated. In the knives wherethe blade was secured to the knife by confronting wedging surfaces, theblade vibration caused the blade to shift axially into undesired contactwith the blade housing. This axial blade movement contributed both toknife vibration and blade heating. In order to constrain the blade torotate about an axis that was relatively fixed with respect to the bladehousing, the blade housing diameter was adjusted to minimize the radialclearance between the radially outer blade body and gear surfaces andthe radially outer race surface. This reduced vibration.

Although vibration was reduced, other problems were created. First,where the blade housing was adjusted to provide a tight runningclearance, heat generated by frictional contact between the blade andblade support was often sufficient to begin to cook the product beingtrimmed. The heated product created a sticky build-up on the knife partsthat generated even more friction heat. In some circumstances, when thehousing diameter was adjusted, the race became slightly out of round, orout of plane. This condition tended to contribute to both vibration andoverheating.

The usual approach to ameliorating these problems was to assemble theblade and housing with running clearances that were tight enough to keepvibration at tolerable levels yet open enough to avoid overheating.Another practice used to reduce vibration and heating was to operate theknife at relatively low rotational speeds. User effort required tooperate the knife increased with lowered operating speeds because theslicing action was reduced. Despite these efforts, the prior art knivestended to both vibrate and run hot. Where operated at low speeds, thevibration and friction heating were accompanied by increased usereffort.

The present invention provides a new and improved annular blade for arotary knife wherein the blade is supported for rotation about a centralaxis at a plurality of line contact bearing locations, resulting in aknife that exhibits minimal vibration and heating and may be operated atrelatively high speeds so that user effort is reduced.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the invention the power operatedknife comprises a blade supporting structure supporting an annular bladefor rotation about a central blade axis. The blade and blade supportingstructure are engagable along bearing contact locations that are spacedapart in a direction parallel to the axis so that the blade isstabilized both radially and axially as the knife operates.

The rotary knife blade comprises an annular body disposed about thecentral axis and an annular blade section projecting from the body. Thebody defines blade bearing surfaces that converge proceeding toward eachother.

In the preferred knife the blade supporting structure comprises a splitblade housing member that is radially expandable and contractible toreceive the blade. The housing member is provided with bead sectionsthat are spaced circumferentially apart about the blade periphery,project into a bearing race formed in the blade, and engage the bladebearing faces as the knife operates. The split blade housing member isadjusted so the blade and housing engage along relatively short lines ofbearing contact that serve to minimize blade-housing friction—andconsequential blade and housing heating—when the knife operates. Thespaced bead sections stabilize the blade as it rotates by providing aseries of bearing locations that are spaced apart both circumferentiallyaround the blade perimeter and in the direction of the axis. The bladerotation axis is thus maintained substantially stationary relative tothe knife so that knife operation is virtually vibration free. Becausethe blade is suspended by the bearing locations, the blade and housingremain spaced apart except at the bearing locations even if the bladehousing suffers from out-of-round and/or “out-of-plane” distortions.

Other features and advantages of the invention will become apparent fromthe following description of a preferred embodiment made in reference tothe accompanying drawings, which form a part of the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a power operated knife incorporating ablade constructed according to the invention;

FIG. 2 is an elevational view of the knife of FIG. 1 with portionsillustrated in cross section;

FIG. 3 is a perspective view of a blade support structure forming partof the knife of FIGS. 1 and 2;

FIG. 4 is an elevational view seen approximately from the planeindicated by the line 4-4 of FIG. 3;

FIG. 5 is a view seen approximately from the plane indicated by the line5-5 of FIG. 4;

FIG. 6 is a cross sectional view seen approximately from the planeindicated by the line 6-6 of FIG. 5;

FIG. 7 is an enlarged fragmentary view of part of the blade supportstructure of FIG. 6;

FIG. 8 is a cross sectional view seen approximately from the planeindicated by the line 8-8 of FIG. 4;

FIG. 9 is an enlarged fragmentary cross sectional view of part of theknife shown in FIG. 1 seen approximately from the plane indicated by theline 9-9 of FIG. 1;

FIG. 10 is a view, similar to FIG. 5, showing a modified knife embodyingthe invention;

FIG. 11 is an enlarged cross sectional view of part of the blade supportstructure of FIG. 10 seen approximately from the plane indicated by theline 11-11;

FIG. 12 is an enlarged cross sectional view of part of the blade supportstructure of FIG. 10 seen approximately from the plane indicated by theline 12-12;

FIG. 13 is an enlarged cross sectional view of part of the blade supportstructure of FIG. 10 seen approximately from the plane indicated by theline 13-13;

FIG. 14 is an enlarged fragmentary cross sectional view, similar to FIG.9, of the modified knife with the blade assembled to the blade support.

FIG. 15 is a perspective view of part of another modified knifeembodying the invention; and,

FIG. 16 is a cross sectional view seen approximately from the planeindicated by the line 16-16 of FIG. 15.

DESCRIPTION OF THE BEST MODES CONTEMPLATED FOR PRACTICING THE INVENTION

A power operated knife 10 constructed according to a preferredembodiment of the invention is illustrated by FIGS. 1 and 2 of thedrawings as comprising a handle 12, a headpiece 14, a blade supportstructure 16 and an annular blade 20.

The knife 10 is connected to a remote electric motor via a flex shaft 21that extends into the handle 12 and transmits drive from the motor tothe blade 20. The motor and flex shaft may be of any conventional orsuitable construction and are not illustrated or described in detail.The flex shaft is sufficiently supple that the user of the knife,grasping the handle, moves the knife with ease and accuracy whileslicing or trimming meat, or removing meat from bones, etc. The handle12 and headpiece 14 may be of any conventional or suitable constructionand are therefore not described in detail. Although an electric motordriven knife is disclosed, the knife could as well contain a pneumaticmotor in the handle 12 and be connected to a compressed air supply by asuitable hose.

The blade support structure 16 supports the blade 20 for rotation aboutits central axis 22 with the blade and blade support structure engagableat least at bearing locations that are spaced axially apart (i.e. spacedapart proceeding in the direction of the axis 22). In a preferredembodiment the bearing locations are defined by circumferential linesegments. The bearing line segments assure that the blade and bladesupport structure engage only along extremely small contact areas. Theaxially spaced apart bearing line segments assure that the blade ispositively supported against lateral and axial vibrations relative tothe blade support structure while frictional resistance to bladerotation afforded by the bearing contact is minimized—thus minimizingheat build-up in the knife. As best illustrated by FIG. 9, the axiallyspaced bearing locations suspend the blade so that the blade and bladesupport structure remain spaced apart except for the bearing locations.

The illustrated blade support structure 16 forms a split ring-likestructure that comprises an annularly curved body section 30 extendingabout the blade 20 and an axially extending mounting section 32 forsecuring the blade support structure 16 to the headpiece. See FIGS. 2-4.The body section 30 extends substantially completely about the bladewith the split 33 centered with respect to the headpiece. The mountingsection 32 extends axially from the body section 30 and detachablyconnects the body section to the headpiece.

The mounting section 32 is illustrated as a circularly curved wall-likestructure that confronts the headpiece with the split 33 extendingcentrally through it. The mounting section 32 defines open endedmounting slots 34 on opposite sides of the split 33 that receivemounting screws 36 (FIG. 2) for securing the blade support structure inplace on the headpiece. The slots 34 are significantly wider than thescrew thread diameters. The mounting screw heads 38 are substantiallywider than the slots. The screw heads engage the mounting section 32 onboth sides of the associated mounting slots 34 to securely clamp theblade support structure in place against the headpiece when the screwsare tightened down. The mounting section central portion 40 essentiallycovers the adjacent headpiece face and, as such, covers a blade drivingpinion gear 41 (FIG. 2) that is mounted in the headpiece and driven fromthe flex shaft 21. The central portion face that confronts the headpieceis machined to provide a planar face confronting the pinion gear 41 sothe central portion wall thickness gradually diminishes proceedingtoward the split 33 (see FIG. 3). The curved headpiece face and theconfronting curved mounting section faces on opposite sides of thecentral portion 40 define mating grooves and lands that extendcircumferentially relative to the blade support structure to assure thatthe blade support structure is securely aligned with and supported bythe headpiece.

The body section 30 retains the blade assembled to the knife whilesupporting the blade for stable, low friction, high speed rotationdespite the application of various forces encountered during knifeoperation. The body section 30 defines a circumferentially extendinggroove, or groove-like space, 42 that receives the blade 20 when theblade is assembled to the knife (see FIGS. 7 and 9). The groove isformed in part by a radial body section wall 44 disposed in a plane thatextends normal to the blade axis 22, an outer peripheral wall 46 thatextends about the blade periphery, and a blade retaining bearingstructure 47 that extends radially inwardly from the wall 46 forengagement with the blade 20. The walls 44 and 46 are cut away on eitherside of the split 33 to provide a semicircular clearance space 48 (FIGS.3, 4 and 6) for the pinion gear 41.

The blade 20 comprises an annular body 50 disposed about the centralaxis 22 and an annular blade section 52. In the illustrated embodimentof the invention (FIG. 9) the body 50 defines first and second axialends 56, 58. The blade section 52 projects axially from the first axialend 56.

The body 50 is comprised of gear teeth 60 forming the second axial bodyend 58 remote from the blade section 52, a wall 62 defining a radiallyouter surface 64 disposed between the body ends 56, 58, and an annularbearing race, or groove, 66 opening in the surface 64. The illustratedgear teeth 60 are cut through the wall 62 to form a ring gear extendingabout the body end 58. The gear teeth 60 are disposed in the bladesupport groove 42 adjacent its walls 44, 46 so the pinion gear and thering gear mesh in the clearance space 48. The ring gear runs in meshwith the driving pinion gear 41 when the knife 10 operates.

The bearing race 66 receives the bearing structure 47 so that the bladebody 50 is secured to the blade support structure by the bearing raceand bearing structure engagement along bearing locations that are spacedaxially apart and firmly support the blade against axial and radialshifting during use. The bearing race 66 extends into the wall 62 and isspaced axially from the blade section 52 in that the surface 64 extendsbetween the bearing structure 47 and the blade section 52.

The bearing race 66 comprises a first and second bearing surfaces 70, 72that converge proceeding toward each other. In the illustrated knife therace extends radially inwardly into the wall 62. The bearing surface 70converges proceeding away from the second axial end 58, and the secondbearing surface 72 converges proceeding toward the first bearing surface70. In the illustrated blade, the surfaces 70, 72 are frustoconical. Asshown, they are joined at their radially inner ends by a short axiallyextending annular surface 74 that serves to minimize the race depth anddoes not engage the bearing structure 47.

The blade section 52 is of conventional or suitable construction and, asillustrated, is formed by radially inner and outer surfaces 90, 92 thatconverge toward each other proceeding away from the body 50 toward acutting edge 94 at the projecting blade end. In the illustrated knifethe edge 94 is formed by the juncture of the surface 90 and a surface 96that extends between the surfaces 90, 92. The surfaces 90, 92 areillustrated as continuous with the blade body 50 and since the surfaces90, 92 converge, the wall thickness of the blade section is less thanthat of the body 50. Although a particular blade configuration isdisclosed, various annular blade configurations are commonly used inpower operated knives depending on the particular use to which the knifeis put. Any such blade configuration may be used with a knife embodyingthe invention.

In the preferred and illustrated embodiment of the invention the bladeand blade support structure engage along lines of bearing contact at afirst plurality of circumferentially spaced apart bearing locationsdisposed in a plane that is transverse to the axis 22, and at a secondplurality of circumferentially spaced apart bearing locations disposedin a second plane that is spaced from the first plane and extendstransverse to the axis 22. In the illustrated knife 10 the bearingstructure 47 is formed by at least three radially inwardly projectingbeads 100 that are spaced circumferentially apart about the bladesupport structure. See FIGS. 5, and 7-9. Each illustrated bead has asemicircular cross sectional shape (see FIG. 9) so that each bead firmlyengages the frustoconical surfaces 70, 72 along the respective arcuatebearing contact line segments 102, 104 (FIG. 9). In the illustratedknife, four beads 100 a, 100 b, 100 c, 100 d, are formed about the bladesupport body section.

The use of multiple beads assures that, when the blade support structureis tightened about the blade, spaced apart beads move into snugengagement with the blade bearing race. This relationship exists evenwhere the blade support structure suffers from out-of-round orout-of-plane distortions created during manufacturing or as a result ofimproper blade support structure size adjustment.

In the knife illustrated by FIGS. 1-9 the blade support structure isinitially formed with a continuous, radially inwardly extending bead.The bead sections 100 a-d are formed by a machining operation thatremoves sections of the original bead, leaving a cylindrically curvedsurface spaced from the blade periphery.

The beads 100 a, 100 b extend from opposite sides of the split 33 andsupport the blade against gear induced reaction forces that urge theblade 20 away from the pinion gear 41 when the knife is operating. Theblade race surface 70 thus tends to bear forcefully on the beads 100 a,100 b in the vicinity of the pinion gear 41. The beads 100 a, 100 b arerelatively longer than the beads 100 c, 100 d so that the gear reactionloads are distributed relatively widely. Although the gear reactionloads tend to force the blade 20 in a direction away from the piniongear, the beads 100 a, 100 b prevent axial blade deflection and remainin bearing engagement with both race bearing surfaces 70, 72. Thisconstrains the circumferential section of the blade 20 near the piniongear against axial and radial shifting. In the blade support structure16 illustrated by FIG. 8, the beads 100 a, 100 b subtend equal arcs ofabout 58° around the axis 22.

The beads 100 c, 100 d are disposed diametrically opposite from thebeads 100 a, 100 b and remote from the headpiece. See FIG. 8. The beads100 a-d bear firmly on the surfaces 70, 72 to maintain the blade 20radially centered on the axis 22 and fixed against displacement in anaxial direction. When the knife is being operated to slice meat or fatfrom a larger animal part the circumferential section of the blade inthe vicinity of the beads 100 c, 100 d tends to be forced toward theradial blade support member wall 44. Engagement between the bearing face72 and the beads 100 c, 100 d precludes axial blade deflection fromforces exerted by slicing and trimming meat, etc. The radial componentof deflection force is reacted against by the beads 100 a, 100 b tomaintain the blade radially stabilized. The illustrated beads 100 c, 100d subtend arcs of about 34° around the axis 22, respectively.

FIGS. 10-14 are illustrative of a modified knife that embodies thepresent invention. The knife of FIGS. 10-14 is constructed like theknife 10 except for the blade support structure 120 and blade 122.Accordingly, only the blade support structure 120 and blade 122 areillustrated and described in detail to the extent they differ from theblade support structure 16 and blade 20. Reference should be made toFIGS. 1-9 and the associated description for details of the remainingparts of the knife of FIGS. 10-14. Parts of the blade support structure120 and blade 122 that are the same as parts of the blade supportstructure 16 and blade 20 are indicated by corresponding primedreference characters.

The blade support structure 120 supports the blade 122 for rotationabout its central axis 124 with the blade and blade support structureengagable at least at spaced apart bearing locations proceeding in thedirection of the axis 124. The axially spaced bearing locations suspendthe blade so that the blade and blade housing remain spaced apart exceptfor the bearing locations. See FIG. 14.

The blade support structure 120 is constructed substantially like theblade support structure 16 except that its outer peripheral wall 130defines a series of circumferentially spaced apart, radially thickenedwall sections 132. The wall sections 132 define radially inwardly facingfrustoconical bearing faces 133, 134 that are substantially centered onthe axis 124 and converge proceeding in opposite axial directions. Thesebearing faces are engaged by bearing bead surfaces on the blade alongnarrow lines of contact. In the preferred embodiment the bearing faces133, 134 form walls of inwardly opening grooves formed in each thickenedwall section 132. The portions of the peripheral wall 130 between thethickened sections are relieved and spaced away from the blade beadsurfaces at all times (FIG. 13).

The blade support structure 120 may be formed by machining a radiallyinwardly opening groove completely around the inner periphery of theperipheral wall 130 to define the bearing faces 133, 134. The thickenedsections are then formed by machining the wall 130 to provide relieved,thin wall sections 135 between the sections 132 (see FIGS. 11-13).

The blade support structure illustrated in FIG. 11, et seq. has fourthickened sections. Two sections 132 extend oppositely from the split33′ in the blade support structure 120. The remaining two thickenedsections are located on the diametrically opposite side of the bladesupport structure. The bearing faces may be distributed about the axis124 in any suitable pattern. Further, there may be more or fewer thanfour thickened sections.

The blade 122 is like the blade 20 except that the bearing race 66 ofthe blade 20 is replaced by a bearing bead 140 extending continuouslyabout the blade periphery and projecting radially into contact with thebearing faces 133, 134. The bead 140 has a semicircular cross sectionalshape so it defines bearing surfaces that converge proceeding towardeach other and contacts the support housing bearing faces 133,134 alonglines of bearing contact 102′, 104′ that extend the length of thegrooves.

The bearing contact line segments assure that the blade and bladesupport structure engage only along extremely small contact areas. Theaxially spaced apart bearing contact line segments assure that the bladeis positively supported against radial and axial vibrations relative tothe blade support structure while frictional resistance to bladerotation afforded by the bearing contact is minimized.

The blade support structure 120 is tightened about the blade with thebearing faces 133, 134 contacting the bead 140 and suspending the bladeso it does not make contact with the blade supporting structure exceptat the lines of bearing contact (FIG. 14). When positioned as desired,the blade support structure 120 is fixed in position by clamping screwslike the screws 36.

FIGS. 15 and 16 illustrate still another knife construction that is thesame as the knife 10 of FIGS. 1-9 except for the blade support structure160. The blade support structure 160 is constructed the same as theblade support structure 16 except that six bearing bead sections 200 a,200 b, 200 c, 200 d, 200 e, and 200 f are provided to establish bearingcontact with the blade, rather than the four bearing beads provided bythe blade support structure 16. The blade used with the blade support160 is identical to the blade 20 and is therefore not illustrated. Partsof the blade support structure 160 that are identical to parts of theblade support structure 16 are indicated by corresponding referencecharacters and are not described further.

The bearing bead sections 200 a, 200 b extend from opposite sides of thesplit 33 and support the blade against gear induced reaction forces thaturge the blade 20 away from the pinion gear 41 when the knife isoperating. The beads 200 a, 200 b occupy the same arc lengths as thebeads 100 a, 100 b and are relatively longer than the beads 200 c-200 fso that the gear reaction loads are distributed relatively widely.Although the gear reaction loads tend to force the blade 20 in adirection away from the pinion gear, the beads 200 a, 200 b preventaxial blade deflection and remain in bearing engagement with both bladerace bearing surfaces 70, 72. The circumferential section of the blade20 near the pinion gear is constrained against axial and radial shiftingby the bead and race engagement. In the blade support 160 illustrated byFIGS. 15 and 16, the beads 200 a, 200 b subtend equal arcs of about 58°around the axis 22.

The beads 200 c, 200 d are disposed diametrically opposite from thebeads 200 a, 200 b and remote from the knife headpiece. The beads 200 c,200 d are identical to the beads of the knife of FIGS. 1-9 and arespaced apart the same arc length i.e. each subtends an arc of about 34°around the axis 22 and the beads are spaced about 34° apart.

The bead 200 e is centered between the beads 200 a, 200 c while the bead200 f is centered between the beads 200 b, 200 d. See FIG. 15. The beads200 e, 200 f subtend arcs of about 35°, respectively. The beads 200 c-fbear firmly on the blade bearing race surfaces 70, 72 to maintain theblade 20 radially centered on the axis 22 and fixed against axialdisplacement.

The beads 200 a-f coact with the bearing faces 70, 72 and with eachother to preclude both axial and radial blade vibrations. Any tendencyfor one circumferential portion of the blade 20 to deflect axiallycreates an axial and a radial component of reaction force applied to theblade by the bead engaging the affected circumferential blade portion.The radially directed force, which might otherwise shift the bladeradially away from the bead, is reacted against by one or more beadslocated on the diametrically opposed side of the blade so that no radialblade motion occurs. This obviates blade vibrations.

Knives equipped with the blade support structure 160 may exhibit alonger effective blade life than those equipped with the blade supportstructure 16. When the beads 100 a-100 d wear as a result of extensiveuse, the blade 20 might be able to contact the blade support bodysection 30 in the space between the beads 100 a and 100 c, or betweenthe beads 100 b and 100 d during use. This would cause blade wear andnecessitate eventual replacement. When knives equipped with the bladesupport structure 160 experience the same amount of wear on the beads200 a-d, the bead 200 e or the bead 200 f preludes the blade 20 fromcontacting the body section 30, thus avoiding blade wear. The amount ofheat generated by the blade support structure 160 has not been observedto be greater than that generated by the blade support structure 16.

The beads 100 and 200 that are illustrated in connection with FIGS. 1-9,and FIGS. 15 and 16, respectively, are located symmetrically about aline 202 extending through the split 33 and the diametrically oppositeside of the blade support body section 30. It should be appreciated thatthe beads 100 a-d or the beads 200 a-f could be distributed in differentconfigurations about the body section 30, and have different arc lengthsfrom those noted above, depending on what use the knife 10 is to be put.Furthermore, three beads, five beads, or more than six beads, might beemployed depending on knife usage.

In theory, even a single bead, extending substantially about the blade20, could be employed in the knife 10 so long as the blade 20 wassupported substantially about its periphery at axially spaced bearinglocations. In practice, such a construction is problematical because theblade support structure would have to be radially expansible to permitblade removal and replacement. Adjusting the blade support structurediameter so that the blade is uniformly and firmly engaged by a singlebead about its periphery is difficult. The blade tends to be engaged atone or two random locations resulting in radial and axial bladevibration. Furthermore, where the blade is snugly engaged by the supportstructure substantially about its periphery, blade heating during use isgreater than experienced with multiple bearing beads because the singlebead contacts the bearing surfaces 70, 72, over longer lengths.

While different embodiments of the invention have been illustrated anddescribed, the invention is not to be considered limited to the preciseconstructions shown. Various modifications, adaptations, and uses of theinvention may occur to those having ordinary skill in the business ofconstructing power operated rotary knives. The intention is to coverhereby all such modifications, adaptations and uses that fall within thescope or spirit of the appended claims.

1. A blade support structure for a rotatable annular knife blade, saidblade support structure comprising an annular curved body sectionextending circumferentially about a central axis and being split toprovide for radial expansion and contraction of the body section, thebody section including a circumferentially extending groove which facesradially inwardly and a blade retaining bearing structure projectingradially inwardly adjacent the groove, the blade retaining bearingstructure including at least a first bearing location defining a firstbearing contact line in a plane that is transverse to said central axis,and at least a second bearing location defining a second bearing contactline that is spaced axially from said first bearing contact line,wherein portions of the blade retaining bearing structure forming thefirst and second bearing contact lines are substantially semicircular incross section with respect to the inwardly projecting blade retainingbearing structure.
 2. The blade support structure claimed in claim 1wherein the blade retaining bearing structure includes a bearing beadprojecting radially inwardly from an outer peripheral wall of the bodysection and wherein said first and second bearing contact lines areformed by the bearing bead.
 3. The blade support structure claimed inclaim 1 wherein the blade retaining bearing structure includes aplurality of circumferentially spaced apart bearing beads eachprojecting radially inwardly from an outer peripheral wall of the bodysection and wherein said first and second bearing contact lines areformed by the plurality of bearing beads.
 4. A combination of a bladesupport structure and a rotatable annular knife blade comprising: theannular knife blade adapted to be inserted and removed from the bladesupport structure; and the blade support structure including an annularcurved body section extending circumferentially about a central axis andbeing split to provide for radial expansion and contraction of the bodysection for insertion and removal of the knife blade from the bladesupport structure, the body section including a blade retaining bearingstructure, the blade retaining bearing structure including a firstbearing location defining a first bearing contact line with the blade ina plane that is transverse to the central axis, and at least a secondbearing location defining a second bearing contact line with the bladein a plane that is spaced axially from said first bearing contact line,the blade and blade support structure being engaged along the first andsecond bearing contact lines.
 5. The combination of a blade supportstructure and a rotatable annular knife blade as set forth in claim 4wherein the blade retaining bearing structure includes a bearing beadprojecting radially inwardly from an outer peripheral wall of the bodysection and wherein the first and second bearing contact lines areformed by the bearing bead.
 6. The combination of a blade supportstructure and a rotatable annular knife blade as set forth in claim 4wherein the blade retaining bearing structure includes a plurality ofcircumferentially spaced apart bearing beads each projecting radiallyinwardly from an outer peripheral wall of the body section and whereinsaid first and second bearing contact lines are formed by the pluralityof bearing beads.
 7. The combination of a blade support structure and arotatable annular knife blade of claim 4 wherein portions of the bladeretaining bearing structure forming the first and second bearing contactlines are substantially semicircular in cross section with respect tothe inwardly projecting blade retaining bearing structure.